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Fish prefer plastic to natural prey

Larval perch from the Baltic Sea that has ingested microplastic particles

Photograph: Oona Lönnstedt

When grown, fish that were exposed to microplastics as larvae prefer to eat plastic rather than their natural prey and are less active and responsive to predator cues, threatening the sustainability of entire species, according to research published today (3 June).

A study by researchers at Uppsala University in Sweden, published in the Science journal, exposed Eurasian perch larvae to ‘environmentally relevant concentrations of microplastic polystyrene particles’, and found that they exhibited changed behaviours and stunted growth that led to ‘greatly increased mortality rates’.

Fish ignored natural food source in favour of plastic

Researchers that carried out today’s study say that it is the first that is ‘able to show that development of fish is threatened by microplastic pollution’.

The larvae exposed to microplastics experienced stunted growth as they seemed to show a preference for the plastic and completely ignored their natural food source of free-swimming zooplankton.

This lack of nutrition also made the fish less active and their diminished anti-predator response made the larvae more vulnerable to predators. Indeed, when the perch were placed together with a natural predator (pike), fish that had been exposed to microplastic particles were caught and eaten more than four times quicker than control fish, with all fish exposed to microplastic particles dead within 48 hours.

Microplastic effect on aquatic ecosystems could be ‘profound’

If the response of the perch larvae translates to the wider marine population, the study concludes, there could be direct consequences for the replenishment and sustainability of fish populations.

Marine biologist Dr Oona Lönnstedt, lead author of the Science article, said: “The microplastic particle levels tested in the current study are similar to what is found in many coastal habitats in Sweden and elsewhere in the world today.

“If early life-history stages of other species are similarly affected by microplastics, and this translates to increased mortality rates, the effects on aquatic ecosystems could be profound.”

Professor Peter Eklöv, co-author of the study, added: “This is the first time an animal has been found to preferentially feed on plastic particles and is cause for concern.

“Increases in microplastic pollution in the Baltic Sea and marked recruitment declines of the coastal keystone species, like perch and pike, have recently been observed. Our study suggests a potential driver for the observed decreased recruitment rate and increased mortality.”

Growing awareness of microplastics’ impacts

Though the researchers say that more comprehensive studies are required before any far-reaching conclusions can be drawn, they are clear that the findings highlight the need for new management strategies or alternative biodegradable products that lower the release of microplastic waste products.

This Eunomia graphic shows the extent of microplastic pollution in the marine environment

Graphic: Eunomia Research and Consulting

Awareness of the environmental impact of non-biodegradable microplastic particles, defined as pieces of plastic that are less than five millimetres in size, has been growing in recent years. Among the largest causes of microplastic pollution are microbeads used in cosmetics and personal care products, though they are also created by the fragmentation of large plastic products that have been littered or exposed to waterways, as well as by the shedding of synthetic fabrics when washing clothes.

Figures released by Eunomia Research & Consulting last week estimated that, globally, 950,000 tonnes of microplastics enter the marine environment every year. Scientists are just beginning to research the effect of plastics entering the food web, although research has confirmed that many fish have ingested microplastics, and around 35 per cent have microplastics in their stomach that they cannot excrete, according to a Convention on Biological Diversity study.

The study report, ‘Environmentally relevant concentrations of microplastic particles influence larval fish ecology’, can be found in the new issue of Science, and more on the effect that plastic litter has on the marine food web can be found in Resource’s feature article.